1. Field of the Invention
The present invention relates to an oxygen sensor using the principle of surface plasmon resonance (SPR) and an oxygen transmission rate (OTR) measurement system including the oxygen sensor.
2. Description of the Related Art
With the recent development of displays in terms of materials and structures, the demand for sensors having functions which have not been provided before is increasing. In this regard, there is exemplified an organic light emitting device (OLED) as a flat display. The OLED is receiving attention as a next-generation display which is solely for emitting light. The display includes materials and structures having electrical, mechanical and optical properties. In the OLED, organic material may cause a danger of impairment attributable to reaction with water vapor and oxygen. Thus, because the OLED must maximally block out water vapor and oxygen which have a direct influence on the lifespan thereof, a highly blockable substrate, a sealing material, and an enclosing material or the like is employed.
Hence, as the evaluation of a material or structure having a very low gas transmission rate is required, methods therefor have been developed. The measurement of the transmission rate of the material and structure requires a measurement tool having high sensitivity, in particular, a gas sensor able to evaluate a very low gas transmission rate.
As an example of the sensor, an IR gas sensor is disclosed in U.S. Pat. No. 6,067,840 granted to Texas Instruments Inc. To determine the concentration of gas to be monitored, differential absorption between two IR sources respectively disposed toward a sensing gas and a reference gas is applied. As another example, U.S. Pat. No. 6,460,405 granted to MOCON, Inc. discloses a gas sensor, in which a measuring sample is exposed to a chemically inert tracer gas such as helium or carbon dioxide, and which includes a tracer gas detector for measuring the flow of tracer gas through the sample, the measured value being related to a gas transmission rate of the experimental sample.
With regard to SPR useful in the present invention and quite different from the above techniques, general SPR-based sensors including a transparent prism and a metal film applied to a thickness of about 50 nm thereon and methods of measuring changes in the dielectric constant or refractive index corresponding to changes in a sample on the metal film have been proposed. First, U.S. Pat. No. 4,889,427 discloses a method of measuring a resonance angle and its change while changing an incidence angle θ using the incident light of a monochromatic light source and a prism having a predetermined refractive index.
Second, U.S. Pat. No. 5,359,681 discloses a method of measuring changes in wavelength depending on resonance conditions using a light source having multiple wavelengths including white light at an incidence angle θ within a limited range.
Third, U.S. Pat. No. 4,844,613 discloses a method of measuring a resonance angle without a rotational driver using a multi-channel light receiving device such as a photodiode array (PDA) while a light source of an expanded single wavelength is focused on the center of a medium.
These days, techniques using local surface plasmon effects occurring not with a metal film but with metal nanoparticles have been devised. In the case where the metal nanoparticles are dispersed in a dielectric material, local field enhancement occurs due to SPR caused by the metal nanoparticles, resulting in very large optical nonlinearity.
The use of a glass substrate for a microscope coated with metal nanoparticles as a sensor substrate includes T-LSPR (Transmission Localized Surface Plasmon Resonance Spectroscopy) or P-SPR (Propagating Surface Plasmon Resonance Spectroscopy) As such, T-LSPR employs a sensor including a transparent substrate coated considerably thinly with a film or metal nanoparticles. T-LSPR shares the same basic principle as that of P-SPR with the exception that the sensor substrate is manufactured slightly differently, and is used to measure, using a UV-visible spectrometer, changes around the sensor based on changes in SPR absorption coefficient after application of an oxygen-sensitive organic material on the sensor substrate including transparent glass coated with metal nanoparticles.